Diseased Hoya Leaves

Diseases

• Botrytis blight (Botrytis cinerea) and stem rot (Rhizoctonia spp.) are fungal diseases that affect the stems and leaves of hoya plants. Erwinia carotovora is a bacterial disease that attacks the leaves of hoyas, although hoyas may only play the role of host plant until this disease finds a more suitable plant to attack. The tomato spotted wilt virus (of which there are many different strains) can infect hoyas after an attack by thrip insects.

Symptoms

• Botrytis blight appears as grayish spots on the leaves near the center of the plant. Rhizoctonia may be slow to show up, but will appear as reddish-brown webs and rotting leaf tissue. Erwinia bacteria on hoya leaves starts as pinprick spots developing into haloed spots that are yellow to tan. Tomato spotted wilt virus has many symptoms and are very different on the many plant species they infect. The most telling sign is enation, or outgrowths on the surface of the leaves, especially when paired with leaf yellowing or browning.

Prevention

• Fungal diseases develop best in areas with poor ventilation, infected soils and too-frequent watering. Correcting these issues before planting is key. Erwinia bacteria is transmitted through cuts or damaged areas. Disinfecting all tools between each use and each plant as well as purchasing healthy-looking hoyas from trusted suppliers prevents most bacterial problems. Since tomato spotted wilt virus cannot be vectored by any other host except thrips, preventing and eradicating thrip populations on or near hoyas is the best preventative measure.

Remedies

• Getting the disease properly identified by the local extension service is the first step to proper treatment. Many fungicides such as copper and sulfur suppress or control fungal leaf diseases on hoyas, provided all package instructions are followed. Remove and destroy diseased plant parts or heavily diseased plants. There are no reliable cures for Erwinia bacteria or tomato spotted wilt virus.